The Secret Animal Society needs to help an old friend - Spike. The Secret Animal Society - an organisation which protects those very rare animals few people know even exist - is located in a remote valley close to the sea. When twins Eddie and Izzie move there with their family, they're very disappointed that many of the animals keep themselves hidden. In fact, the only one they see regularly is Cornflake the dragon. Noah, the old caretaker, tells them that it's normal - there are some creatures that they haven't seen for years. Then there's a sighting of an unidentified creature far out at sea, which seems to be heading to the sanctuary. The media goes into a frenzy - is it some sort of sea monster, a giant squid or octopus, perhaps? But it's really a sea serpent (a plesiosaur). Noah recognises its song - it's Spike, one of his favourite animals who no one's seen for years. But now Spike is returning to the society, and it sounds like he's in distress. It turns out he's got his baby with him, who's sick, and he's hoping the society can help.